1. Field of the Invention
The invention relates to an engine starting system and an engine starting method. More particularly, the invention relates to technology for starting an engine mounted in a vehicle that is able to run using torque output from an electric motor.
2. Description of the Related Art
A hybrid vehicle provided with an engine and an electric motor as drive sources is known. The hybrid vehicle is provided with a power storage device such as a battery that stores electric power to be supplied to the electric motor. Electric power generated by a generator driven by the engine and electric power regenerated using the electric motor during deceleration of the vehicle, for example, are stored in the battery. In a plug-in hybrid vehicle, the battery is also able to be charged with electric power supplied from an external power supply outside the vehicle.
A hybrid vehicle is able to run using one or both of the engine and the electric motor as the drive source according to the operating state of the vehicle and the like. Therefore, when the state-of-charge (SOC) of the battery is large, for example, the engine may be stopped and the vehicle may be run using only the electric motor as the drive source. The driver may also be able to select a mode to run using only the electric motor as the drive source by operating a switch.
Therefore, in a hybrid vehicle, the time that the engine continues to be stopped, i.e., remains stopped, tends to be long. In particular, in a plug-in hybrid vehicle, if the battery is charged often using an external power supply outside the vehicle, there will be no need to drive the engine to generate power to charge the battery. Therefore, it is possible that the engine will almost never be driven. If the engine is not driven for an extended period of time, the amount of evaporated fuel (vapor) from the fuel tank and the like that is trapped in a canister may become excessive. Also, lubrication may become insufficient because the oil pump is not driven. Therefore, technology that forcibly drives the engine at regular intervals has been proposed.
Japanese Patent Application Publication No. 5-270294 (JP-A-5-270294) describes a control apparatus for an electric vehicle, that forcibly drives an internal combustion engine when it is detected that the internal combustion engine has not been used for a predetermined period of time.
However, if the engine is driven at regular intervals, fuel efficiency may decrease from driving the engine.